(1) Field of the Invention
The present invention relates to a method and device for inhibiting oil leakage from an electric motor and, more particularly, to a bearing cap having one or more protuberances thereon dimensioned to prevent a motor shaft washer from moving into contact with an inner rim of the bearing cap, and to an electric motor embodying such a bearing cap.
(2) Description of the Related Art
A conventional electric motor configured for a shaft-down application (i.e., where the motor shaft extends vertically downward through the motor housing) is shown generally in FIG. 1, and includes an end shield A, a motor shaft B, a rubber washer C, a bearing cap D, and an oil wick E. The bearing cap, which together with the end shield forms a portion of the motor housing, includes an opening F through which the motor shaft can extend, and holds the rubber washer within the electric motor when the motor is fully assembled. One primary function of the bearing cap is to catch oil that travels through openings G formed in the end shield, as well as to catch any oil that travels down through the end shield between the motor shaft and an end shield hub H. The oil wick is provided for drawing oil contained in the bearing cap back to an opposite side of the end shield. FIG. 1 also illustrates several centering tabs I formed on the end shield for maintaining the rubber washer in alignment with the motor shaft during assembly of the electric motor.
When the electric motor is fully assembled as shown in FIG. 2, the rubber washer extends around the motor shaft and maintains positive clearance with both an inner rim J of the bearing cap and the end shield hub. Thus, the rubber washer rotates freely with the motor shaft and holds tight thereto for preventing oil from running down the motor shaft and through the bearing cap opening. During the assembly process, the rubber washer is positioned as shown in FIG. 2 using a positioning tool that can slide between the motor shaft and the inner rim of the bearing cap so as to push the washer away from the inner rim. For this reason, the diameter of the bearing cap opening must be large enough to allow not just the motor shaft to extend therethrough, but the positioning tool as well.
The prior art electric motor is disadvantaged in several significant respects, including the tendency of the motor to leak oil when in service. Over time, the rubber washer can move downwardly along the length of the motor shaft and ultimately contact the inner rim of the bearing cap. Thereafter, rotation of the motor shaft induces a pumping action between the bottom side of the rubber washer and the top edge of the inner rim, and pumps oil contained within the bearing cap over the top edge of the inner rim. Once the oil is lifted over the inner rim, it is free to run down the motor shaft, through the bearing cap opening, and out of the electric motor. As is well-known in the art, the loss of oil from an electric motor increases the temperature of the motor bearings and ultimately results in premature motor failure.
When an electric motor of the type described above is configured for a shaft-across application (i.e., where the motor shaft extends horizontally through the motor housing), the washer shown in FIGS. 1 and 2 is not used and, thus, the positioning tool is unnecessary. The added space between the inner rim of the bearing cap and the motor shaft, which was provided for insertion of the positioning tool, is also unnecessary. In fact, for shaft-across motor applications, this added space leaves the electric motor overly exposed to contaminates and moisture that can contaminate the oil and/or induce corrosion, thereby reducing the useable life of the electric motor. Moreover, typical shaft-across electric motors employ a necked-down motor shaft (i.e., a motor shaft having a reduced diameter in the vicinity of the bearing cap opening) to facilitate the assembly process. Such a necked-down motor shaft further increases the spacing between the inner rim of the bearing cap and the motor shaft and, hence, further exposes the electric motor to contaminants and moisture. For all of these reasons, the bearing cap used for shaft-across applications must have a smaller opening than that of the bearing cap used for shaft-down applications.
As explained above, two different types of bearing caps must be manufactured and stocked, where the type of bearing cap used with a given electric motor depends upon whether the motor will be configured for a shaft-down or shaft-across application. The requirement for two different bearing caps increases inventory and handling costs, and also introduces a risk of using the wrong type of bearing cap in a particular assembly, thereby causing quality control problems.
What is needed is a method and device for preventing the rubber washer used in shaft-down motor applications from moving into contact with the inner rim of the bearing cap so as to eliminate the pumping action that can otherwise be induced when the motor shaft is rotating. Such a method and device would preferably eliminate the need for two different types of bearing caps having different sized openings so that a single bearing cap can be used in both shaft-down and shaft-across motor applications. Providing a single type of bearing cap for use in either application would reduce inventory, handling, and other manufacturing costs, and would eliminate the risk of using the wrong type of bearing cap in a particular motor assembly.